Recording tape cartridge

ABSTRACT

A recording tape cartridge which comprises a recording tape wound in a roll on each of a pair of hubs and at least one slip sheet laid to elastically support the roll of the recording tape with a plurality of rib units, each of the rib units being composed of plurality of ribs projected from the slip sheet to form a generally hexagonal configuration in plan view.

FIELD OF THE INVENTION

The present invention relates to a recording tape cartridge which hasslip sheets contained in its cartridge case, and more particularly, toan improvement in the configuration of ribs embossed on the slip sheetsto give excellent cushioning effect to the slip sheets, therebyimproving the state of winding of the recording tape with respect tohubs while reducing frictional sound caused by sliding contact betweenthe slip sheets and tape edges upon running of the recording tape.

BACKGROUND OF THE INVENTION

In a magnetic recording tape cartridge 1 as shown in FIGS. 1 and 2having a magnetic recording tape 3 wound around a pair of hubs 4, inorder to facilitate smooth rotation of the hubs 4 and stable running ofthe recording tape 3, there are interposed slip sheets 5 in one gapbetween the inner surface of a top wall 1a of the tape cartridge 1 andthe top end surface 3a of the roll of the magnetic recording tape 3including the top end surface of the hubs 4 and in another gap betweenthe inner surface of a bottom wall 1b of the tape cartridge 1 and thebottom end surface 3b of the roll of the magnetic recording tape 3including the bottom end surface of the hubs 4.

In such a recording tape cartridge, gaps are defined respectively inwidth of about 0.5 mm. Since the slip sheets 5 are essentially adaptedto fill up the gaps, it is desirable to give cushioning effect to theslip sheets 5, which are elastically brought into contact with the hubend surfaces and the tape edges. Thus, it is well known in the art toemboss the slip sheets 5 with various configurations of projections orribs while curling the slip sheets 5 in a convex manner as shown in FIG.5.

When thus provided with the projections or ribs and curled in a convexmanner, the slip sheets 5 prevent swaying of the hubs 4 and verticalmovement of the recording tape 3, thereby improving the state of windingof the recording tape 3 with respect to the hubs 4 and stabilizing thetape running.

However, there comes into question the configuration of the ribs to beembossed on the slip sheets 5. Depending on the selected configuration,the ribs might be flattened by repeated use, resulting in loss of theiressential function. Further, since the frictional sound is raised byincrease in frictional pressure of the slip sheets 5 against the hub endsurfaces and the tape edges, the configuration of the ribs must beselected to reduce such frictional sound.

In an example of the conventional recording tape cartridge as shown inFIG. 1, the slip sheets 5 are provided with a plurality of projections Pwhich are projectingly formed in a hollow hemispherical configurationover the entire surfaces thereof. Since the respective configurationsare not linked with one another in such a construction, the ribs areliable to be flattened and thus it is difficult to maintain thecushioning effect of the slip sheets for a long period of time. It iswell known in the art that the slip sheets are longitudinally curled ina convex manner as shown in FIG. 5 so that the central highest portionsin the widthwise direction thereof are faced to the end surfaces of thehubs 4 and the end surface of the roll of the recording tape to furtherprevent swaying of the hubs 4 and vertical movement of the recordingtape 3. However, when the projections P are embossed in a dotted manneron such curled slip sheets 5, only the central portions in thelongitudinal and widthwise directions of the slip sheets 5 are apt to bereformed in convexly swollen forms, and the cushioning effect cannot beobtained at the peripheral portions of the slip sheets, and it isdifficult to maintain and/or reinforce the curling of. the slip sheet.Such slip sheets are effective, though, in improving slidability andreducing the frictional sound since contact areas of the hub endsurfaces and the tape edges with respect to the slip sheets are reducedparticularly when the slip sheets are set in place with the surfaces ofthe ribs faced to the hub end surfaces and the tape edges.

Thus, ribs or projections to be embossed on the slip sheets 5 arepreferably continuous in both longitudinal and widthwise directions overthe entire surfaces of the slip sheets 5. For this purpose, there areproposed other slip sheets as shown in FIGS. 9 and 10 in which each ofthe rib units is formed in a triangular configuration 91 (see FIG. 9) ora rectangular configuration 92 (see FIG. 10) in plan view.

However, a series of triangular and/or rectangular ribs 91 and 92 inlinear linkages of the ribs. Consequently, the slip sheets are subjectedto creasing along the linking lines, to reduce strength of the ribs 9themselves. Further, when the slip sheet 5 are curled in theaforementioned convex manner, the central portions in the longitudinaland widthwise directions of the slip sheets are apt to be convexlyswollen similarly to those embossed with the hemispherical projectionsin a dotted manner, and likewise it is difficult to maintain and/orreinforce the curling characteristics. Still further, since the ribs 9are continuous in a linear manner, the frictional sound is spread overthe entire surfaces of the slip sheets, leading to increase of thefrictional sound.

SUMMARY OF THE INVENTION

It is an essential object of the present invention to overcome theaforementioned disadvantages of the prior art by improving theconfiguration of ribs to be embossed on the slip sheet by forminghexagonal unit ribs which are linked in both longitudinal and crossdirections over the entire surface of the slip sheet thereby makinghexagonal patterns.

Another object of the present invention is to provide a recording tapecartridge with improved slip sheets to reduce friction noise between thetape edges and the slip sheets when the recording tape is running.

A further object of the present invention is to provide a recording tapecartridge which enables the take up of the recording tape on a roll withthe tape edges to be aligned at generally the same level.

A further object of the present invention is to provide a recording tapecartridge in which the slip sheets can be prevented from undesireddeformation so as to always elastically support the rolls of therecording tape.

According to the present invention, there is provided a recording tapecartridge which comprises a recording tape wound in a roll on each of apair of hubs and at least one slip sheet laid on one of the innersurfaces of a wall member of the cartridge to elastically support theroll of the recording tape with a plurality of rib units, each of therib units being composed of plurality of ribs projected from the slipsheet to form a hexagonal configuration in plan view with the rib unitscontinued with one another substantially all over the slip sheet.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a partially fragmented top plan view of a conventionalrecording tape cartridge;

FIG. 2 is a cross sectional view taken along the line A--A in FIG. 1;

FIG. 3 is a partially fragmented top plan view of the magnetic recordingtape cartridge according to the present invention;

FIG. 4 is a top plan view of a slip sheet contained in the recordingtape cartridge;

FIG. 5 is a cross sectional view taken along the line B--B in FIG. 4;

FIG. 6 is an enlarged cross sectional view of an essential portion ofthe slip sheet;

FIG. 7 is a fragmented perspective view of the slip sheet;

FIG. 8 is an enlarged cross sectional view showing an essential portionof another embodiment of the present invention; and

FIGS. 9 and 10 are top plan views respectively showing examples ofconventional slip sheets.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 3 and of the drawings, there is shown a magnetic recording tapecartridge according to the present invention, which comprises acartridge case 1 having drive shaft insertion holes 2 in longitudinalleft and right positions thereof and a pair of hubs 4 rotatably mountedin the inner left and right portions thereof for winding a magneticrecording tape 3. The magnetic recording tape 3 is drawn out from onehub 4 along the front surface of the cartridge case 1 to be taken up bythe other hub 4.

As shown in FIG. 4, each of the slip sheets 5 is elongated in thelongitudinal direction substantially in a rectangular form, and hascircular holes 6 corresponding to the drive shaft insertion holes 2 ofthe cartridge case 1 and a rectangular hole 8 corresponding to atransparent windows 7 formed in the top wall 1a and the bottom wall 1bof the cartridge case 1 between the drive shaft insertion holes 2. Theslip sheet 5 is embossed, toward the surface to be in sliding contactwith the tape edges, with a plurality of ribs 9 which are projectinglyformed to be hexagonal in plan view and V-shaped in section, and linkedwith one another in the longitudinal and widthwise directions over theentire surface of the slip sheet 5. Further, the slip sheet 5 is curledin a convex manner when viewed from the widthwise side as shown by lineB--B with the face along the longitudinal direction uncurled such thatthe central portion relative to the widthwise direction thereof is facedto the hub end surface and the tape edge. The unit rib 9 is in the formof a longitudinally elongated equilateral, inequiangular hexagon, tomaintain curling characteristics given to the slip sheet 5. The angle θin FIG. 4 is set at 45°.

The slip sheet 5 is preferably made of a tetra fluoro ethylene resinmixed with carbon black or graphite powder. Since tetra fluoro ethyleneresin is inferior in filmability, such material is formed in a block,from which the respective slip sheets 5 are cut to be curled in theaforementioned manner, and then embossed with the ribs 9. The slip sheet5 may also be made of other plastic sheet material such as polyester,polyethylene or polybutyeneterephthalate, and may be processed to becurled after embossing of the ribs 9.

When the surface of the slip sheet 5 is charged with static electricityby sliding contact with the hub 4 and the recording tape 3, it may leadto an increase in the torque for winding up the magnetic recording tape3 and occurrence of noise in reproduction of the magnetic records. Thus,it is desirable to mix electrically conductive material such as graphitepowder or carbon black in the material of the slip sheet 5 or to coatthe surface of the slip sheet 5 with an electrically conductive film, toreduce the surface electrical resistance of the slip sheet 5 to anallowable range below 10¹³ Ω/cm², preferably below 10¹² Ω/cm², so thatthe slip sheet 5 is not charged with static electricity.

In the magnetic recording tape cartridge as shown in the drawings, gapsg₁ and g₂ are defined between the upper and lower inner wall surfaces ofthe cartridge case 1 and the upper and lower edges of the recording tape3 for interposition of the slip sheets 5 respectively in length of about0.5 mm i.e., 1 mm in total. Therefore, the height H (see FIG. 5) of thecurled central portion of the slip sheet 5 is preferably set to be about6 mm in a free condition, with a reaction force set to be about 2-5 gwhen the slip sheet 5 is pressed with the height H of 0.5 mm.

The thickness D of the slip sheet 5 itself is selected from a range ofabout 30-200 μm, while the length of one side of the rib 9 is set to beabout 1-10 mm and the height h of projection of the rib 9 is set to beabout 5-200 μm. It is to be noted that the cushioning effect cannot beobtained if the height of the projection of each rib 9 is less than 5μm, while an excess clamping force is applied to the magnetic recordingtape 3 if the height of each rib 9 exceeds 200 μm, resulting in damageof the tape edges and an increase of the frictional sound.

By virtue of the curling formed over the slip sheet 5 and thehexagonally-patterned ribs 9 embossed on the entire surface of the slipsheet 5, an excellent cushioning effect is applied by the slip sheet 5such that the hubs 4 are prevented from swaying while being smoothlyrotated and the magnetic recording tape 3 is prevented from verticalmovement so as to run in a stable manner. Since the substantial contactareas of the surfaces of the slip sheet 5 with respect to the hub endsurfaces and the tape edges are reduced by provision of the ribs 9,slidability thereof is improved to reduce the frictional sound. Even ifrepeatedly used for a long period of time, the ribs 9 reinforce oneanother preventing flattening thereof since the unit ribs 9 are linkedwith one another in the longitudinal and widthwise directions of theslip sheet in hexagonal patterns, thereby stably ensuring long-time use.Further, curling of the slip sheet 5 is effectively maintained in a goodcondition.

Though the slip sheet 5 is formed so as to be curled in a convex mannerin the aforementioned embodiment, the present invention is notnecessarily limited to such a construction. For example, as shown inFIG. 8, the slip sheet 5 may be kept in a flat condition while theprojecting surfaces of the hexagonal ribs 9 are brought into contactwith the inner surfaces of the cartridge case 1 in a butting manner.Though, in this case, the frictional sound is not substantially reduced,the ribs 9 are effectively prevented from flattening, therebyfacilitating development of the cushioning effect of the slip sheet 5.

Needless to say, the present invention can be applied to various typesof recording tape cartridges such as microminiaturized recording tapecartridges, i.e., so-called "microcassette" tape cartridges.

Since the slip sheet 5 according to the present invention is entirelyembossed with the ribs 9 linked in the longitudinal and cross directionsto form hexagonal patterns, the unit ribs 9 reinforce with one anotherby linkage so that the slip sheet 5 is omnidirectionally strengthened,differing from that having triangular or square ribs. Consequently, theslip sheet 5 develops excellent elasticity to prevent swaying of thehubs 4 and vertical movement of the magnetic recording tape 3, therebyimproving the condition of winding of the recording tape 3 with respectto the hubs 4 and improving stability during the tape running. Even ifthe slip sheet 5 is in sliding contact with the hub end surfaces and thetape edges, the slip sheet 5 is effectively prevented from creasing.Further, since the provision of the ribs 9 reduces the substantialcontact areas of the surfaces of the slip sheet with respect to the hubs4 and the tape edges, the slip sheet 5 is also effective in improvingslidability and reducing the frictional sound.

The present invention is now described in further detail with referenceto experimental examples thereof and reference examples.

EXAMPLE 1

A sheet blank having a thickness of 90 μm was cut from a block of tetrafluoro ethylene resin mixed with 15% by weight of graphite powder withcurling effected at a height H of 6 mm in a free condition and reactionforce set about 2-5 g when the slip sheet is pressed to change theheight H of 0.5 mm, and then embossed with equilateral inequiangularhexagonal ribs 9 each having side length of 3 mm and height h of 60 μm,to form the slip sheet 5 as shown in FIG. 4. with the width of 48 mm andthe longitudinal length of 96 mm. The slip sheet 5 was assembled in therecording tape cartridge shown in FIG. 3 in a condition that theconvexly curled portion and the surfaces of the ribs were elasticallybrought into contact with the tape edges.

EXAMPLE 2

A flat sheet of polyester, having thickness of 90 μm, mixed with 15% byweight of graphite powder was embossed with the hexagonal ribs 9 in asimilar manner to Example 1 without effecting the curling to form anon-curled slip sheet 5, which was assembled in the cartridge case 1 ina similar manner to Example 1, except that the surfaces of the ribs 9were brought into contact with the inner wall surfaces of the cartridgecase 1.

REFERENCE EXAMPLE 1

A slip sheet 5 was prepared in a similar manner to Example 1 except thateach of the ribs 9 was prepared in the form of a regular square havingside length of 0.5 mm and height of 60 μm as shown in FIG. 10.

REFERENCE EXAMPLE 2

A flat polyester sheet, having thickness of 90 μm, mixed with 15% byweight of graphite powder was embossed with hemispherical hollowprojections each having a diameter of 1 mm and a height of 60 μm, toform the slip sheet 5, which was assembled in the recording tapecartridge shown in FIG. 1 in a condition that the surfaces of theprojections were brought into contact with the tape edges.

REFERENCE EXAMPLE 3

The slip sheet 5 was prepared by a flat polyester sheet, havingthickness of 200 μm, mixed with 15% by weight of graphite powder withoutcurling nor embossing of the ribs, and was assembled in the recordingtape cartridge shown in FIG. 1.

The recording tape cartridges thus prepared with the aforementionedexamples were mounted on recording/reproducing apparatuses.

The respective recording tape cartridges were mounted onrecording/reproducing apparatuses to run the magnetic recording tapes 3for 300 hours under the normal temperature, and then the magneticrecording tapes 3 were fastly forwarded for measurement of level of themaximum frictional sound caused by the friction of the hub end surfacesand the tape edges with respect to the slip sheets 5 at positions 10 cmremote from the recording/reproducing apparatuses. The results are asfollows:

    ______________________________________                                        Example 1         50 db                                                       Example 2         52 db                                                       Reference Example 1                                                                             56 db                                                       Reference Example 2                                                                             55 db                                                       Reference Example 3                                                                             54 db                                                       ______________________________________                                    

As obvious from these results, the frictional sound was most reduced bythe slip sheet 5 of example 1, though this slip sheet 5 was subjected tocurling, since provision of the ribs 9 reduced the substantial contactareas of the surfaces of the slip sheet 5 with respect to the hub endsurfaces and the tape edges. With respect to example 2, the frictionalsound was reduced to be less than those with respect to referenceexamples 1, 2 and 3, since the slip sheet 5 is not deformed over thewhole, including the ribs 9. With respect to each of examples 1 and 2,further, the range of variation of the frictional sound from thebeginning to the end of winding of the magnetic recording tape 3 withrespect to one hub 4 was small. On the contrary, the level of thefrictional sound was high in each of Reference examples 1, 2 and 3possibly since the slip sheet 5 was deformed, the level of thefrictional sound being made particularly high in the beginning and theend of winding of the magnetic recording tape 3 to the hub 4 due toswaying of the hubs with vertical movement.

Next, the aforementioned recording tape cartridges were mounted onrecording/reproducing apparatuses to run the magnetic recording tape 3for 300 hours under the normal temperature, and then dismantled forobservation of the condition of each part. No disorder nor deformationwas recognized on the slip sheets of examples 1 and 2, and the conditionof winding of the magnetic recording tapes 3 to the hubs 4 werewell-regulated in such a manner that the tape edges on the roll of themagnetic recording tape were aligned generally in a same level to makethe upper end surface and the lower end surface of the roll flat. Saidcondition was particularly excellent in example 1. In example 1,further, curling of the slip sheet 5 was effectively maintained in agood condition. On the contrary, the ribs 91 were partially deformed,and winding of the recording tape 3 to the hubs 4 was considerably outof condition in reference example 2. In reference example 3, the surfaceof the slip sheet 5 in contact with the hubs 4 and the recording tape 3was abraded by sliding contact therewith, and the slip sheet 5 wascreasedly deformed while winding of the recording tape 3 to the hubs 4was remarkably out of condition.

It is to be noted that the slip sheets 5 are not necessarily provided intwo, in the upper and lower portions, and when the recording tapecartridge is a one-sided type, the slip sheet 5 may be provided in one,only in the lower portion of the interior of the cartridge case 1.

The invention being thus described, it will be obvious that the same waybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the present invention, and allsuch modifcations as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

What is claimed is:
 1. A recording tape cartridge complex whichcomprises a recording tape cartridge having a upper and lower wallmember, each with an inner surface, a recording tape with respectiveedges would in a roll on each of a pair of hubs provided on at least oneof said upper and lower wall members of said tape cartridge and at leastone slip sheet comprising apertures corresponding to said hubs laid onat least one of said inner surfaces of at least one of said wall membersof said cartridge to elastically support said roll of the recordingtape, said at least one slip sheet comprising a plurality of rib units,each of said rib units being composed of a plurality of ribs whichproject from said slip sheet to form a hexagonal configuration in planview with said rib units linked in both longitudinal and widthwisedirections over the entire surface of sald slip sheet in such a mannerthat one side of said hexagonal configuration of said respective ribunits forms a common side with an adjoining hexagonal rib unit so as toform a multiplicity of irregular lines corresponding to saidcommon-adjoining sides of said rib units extending from respective endsof said slip sheet.
 2. The recording tape cartridge complex according toclaim 1, wherein the slip sheet is laid on a respective inner surface ofa corresponding wall member of said cartridge such that said ribs face acorresponding tape edge.
 3. The recording tape cartridge complexaccording to claim 1, wherein said slip sheet is curled relative to saidwidthwise direction and non curled along said longitudinal direction. 4.The recording tape cartridge complex according to claim 2, wherein saidslip sheet is curled relative to said widthwise direction and non curledalong said longitudinal direction.
 5. The recording tape cartridgecomplex according to claim 1, wherein said slip sheet is composed of atetraflouoroethylene resin material.
 6. The recording tape cartridgecomplex according to claim 5, wherein said slip sheet is composed totetrafluoro ethylene resin containing graphite powder or carbon black.7. The recording tape cartridge complex according to claim 1, whereinsaid slip sheet has a thickness of about 30 μm to 200 μm, with a lengthof each side of said ribs being 1 to 10 mm and a height of 5 μm to 200μm.
 8. The recording tape cartridge complex according to claim 6,wherein surface resistance of said slip sheet is less than 10¹³ Ω. 9.The recording tape cartridge according to claim 1, wherein each of saidrib units is formed as a longitudinally elongated equilateral,inequiangular hexagon.